240 PEACTICAL PHYSIOLOGY 



CHAPTER XV. 

 CHEMISTRY OF URINE. 



THERE is probably no other portion of Chemical Physiology of greater 

 importance from a clinical standpoint than the chemistry of the urine. 

 It is in the urine that the chief end-products of proteid metabolism 

 (e.g. urea, uric acid, etc.) are excreted, so that a determination of the 

 amount of these will afford us information regarding the activity of 

 chemical interchange in the tissues, of which proteid matter forms the 

 chief part. Again, it is by means of the kidneys that the blood is kept 

 of constant composition, any excess of the normal constituents (e.g. 

 sugar) or any foreign matter (e.g. drugs, unusual proteids) being 

 removed by them and excreted in the urine. In disease of the 

 urinary tract the pathological products (e.g. albumin, blood, cells, etc.) 

 are admixed with the urine and can be detected in it in a more or less 

 changed state, according to the exact site of the lesion. From a 

 purely physiological point of view it is of peculiar interest, since 

 it is in the urine that the incompletely oxidised products of 

 metabolism are excreted, the carbonic acid and water excreted by the 

 lungs representing the completely oxidised. 



In studying its chemistry, therefore, we must ascertain firstly, the 

 nature of the various constituents and their precursors in the blood 

 and tissues ; secondly, the total amount of those excretory products 

 which contain the nitrogen of the decomposed tissue proteid; and 

 thirdly, we must look for unusual products indicating improper com- 

 position of the blood or organic disease of the urinary tract. 



"We . must remember that the quantity and composition of the urine 

 vary considerably within the limits of health, and in order to form 

 reliable conclusions we must collect the total urine for a period of 

 twenty-four hours. Even with a fair sample thus obtained we must 

 consider the intake and loss of water; copious drinking will increase 

 the quantity and lower the specific gravity of the urine ; on the other 

 hand, profuse sweating will have the opposite effect. The nature of 

 the diet in relation to the reaction of the urine and the quantity of 

 urea must also be considered. 



GENERAL CHARACTERS OF URINE. 



Quantity. A healthy man of average weight (65-70 kg.) and height, 

 and living on an ordinary mixed diet, excretes about 1500 c.c. per 

 24 hours. A knowledge of the total daily excretion of urine is in- 



